Table 1.

Demographic and spirometric characteristics of severe COPD subjects from three countries (N [%] or mean ± standard deviation)

	Poland (n=316)	Korea (n=173)	USA (n=339)	p-value for differences between 3 COPD groups
Gender, male	221 (69.9)	172 (99.4)	158 (46.6)	<0.0001
Age	62.4±7.4k,u	68.9±6.2p	68.5±8.3p	<0.0001
BMI	26.8±5.9k,u	21.2±3.1u,p	28.5±6.7k,p	<0.0001
Post-bronchodilator FEV1	0.88±0.32k	0.94±0.27p	0.89±0.28	0.06
Post-bronchodilator FEV1 (%)	30.2±9.4k,u	35.2±8.1p	35.1±8.7p	<0.0001

Note: For continuous variables,

^kcorresponds to significant difference with Korea,

^ucorresponds to significant difference with USA, and

^pcorresponds to significant difference with Poland.

Abbreviations: COPD, chronic obstructive pulmonary disease; BMI, body mass index; FEV₁, forced expiratory volume in 1 second.